The present invention relates to an optical element for a laser, such as a mirror, Brewster window, or the like, and particularly to such an optical element which can be made easily and inexpensively with a clean, chip free mounting edge.
Most lasers have various optical elements, such as mirrors, Brewster windows, prism reflectors and the like, mounted at the ends of the bore tube of the laser. One method of mounting such an optical element, e.g., a mirror, at the end of the bore tube is to form a spherical cavity in the end surface of the bore tube and secure the mirror, which is cylindrical in shape, in the cavity with a suitable bonding material, such as a plastic, such as described in U.S. Pat. No. 3,739,297. This type of mounting provides for ease of adjusting the angle of the mirror with respect to the longitudinal axis of the bore tube. Typically, to mount the mirror in the cavity, the edge of an end surface of the cylindrical mirror is placed in line contact with the surface of the cavity and the mirror is held to the end of the tube by a vacuum on the tube. The mirror is then tilted to the desired angle and the bonding material is applied around the mirror. In order to firmly hold the mirror to the end of the tube while the position of the mirror is being adjusted and to prevent any of the plastic bonding material from being drawn into the tube, there must be no openings between the edge of the mirror and the surface of the cavity. Thus, the mirror must be perfectly cylindrical to provide a perfectly circular edge and the edge must be free of chips or nicks.
The mirrors are generally made by forming individual, small cylinders of high quality optical glass, individually polishing the cylinders and individually applying the desired optical coatings on the mirror surface. To handle each of the mirrors, which are as small as 0.187 inch, individually is difficult and time consuming. Also, to process the mirrors so as to achieve a completely circular, chip free edge is expensive. Furthermore, because of the manner that the individual mirrors are supported when an optical coating is applied to them, the optical coating is not of uniform thickness at the edge of the mirror so that only the center portion of the mirror can be used. Thus, such mirrors as well as other types of optical devices used for lasers are relatively expensive.